The subject matter disclosed herein relates to radiographic imaging, including imaging approaches employing a detector that is not fixed in place.
Digital X-ray imaging systems are becoming increasingly widespread for producing digital data which can be reconstructed into useful radiographic images. In current digital X-ray imaging systems, radiation from a source is directed toward a subject, typically a patient in a medical diagnostic application. A portion of the radiation passes through the patient and impacts a detector that is divided into a matrix of discrete elements, e.g., pixels. The detector elements are read out to generate output signals based upon the quantity or intensity of the radiation impacting each pixel region. The signals may then be processed to generate an image that may be displayed for review.
In certain contexts, a mobile X-ray imaging system may employ a portable detector that is not fixed in position or orientation with respect to the X-ray source. In such contexts, a technician may position the patient and/or portable detector to image the anatomy of interest. In certain circumstances the patient being imaged may be difficult to move or should not be disturbed. Examples of such situations include imaging of newborns or infants in a neonatal intensive care unit (NICU) or of other patients in a critical care type setting, such as a burn unit or intensive care unit (ICU).
In such situations, a mobile imaging system having a portable detector (e.g., a detector that is freely movable relative to the X-ray source) may be employed so that the patient does not have to be moved, and instead the imaging equipment is brought to, and positioned with respect to, the patient. The detector, in such a situation, may be positioned below the patient, such as on a shelf below the patient support surface (e.g., bed) and a single-exposure X-ray image may then be obtained.
In such an approach, only a coarse patient alignment is needed to ensure that the target anatomy is projected onto the detector active area, and will therefore appear in the X-ray image. This coarse alignment may be accomplished based on operator estimation of the placement of the detector based upon a light box shined on the patient during positioning. That is, the path from the X-ray tube head to the projected light box informs the operator about the path of the X-rays and the operator can approximately extrapolate this path to the detector plane.
While this approach may be sufficient for a single-exposure imaging procedure, it is typically not suitable for a tomographic X-ray scan, in which a sequence of offset images are acquired. Such a tomographic scan allows a three-dimensional (3D) view of the patient anatomy to be generated by acquiring this sequence of images (e.g., 5, 10, 15, 20 images) from different views over a limited angular range (e.g., 45°, 60°, 75°, 90°, and so forth). Such a tomographic scan requires additional precise position and orientation information about the source focal spot and detector. However, in contexts where the detector is freely positionable it may not be readily determined if the detector is well-positioned, particularly where the detector is occluded by a table, the patient, blankets covering the patient, or other surface on which the patient is resting cannot be moved.